Method and apparatus for measuring uniformity of tires



Dec. 29, 1970 Q CARR ET AL METHOD AND APPARATUS FOR MEASURING UNIFORMTTYOF TIRES 8 Sheets-Sheet 1 Filed Sept. 5. 1968 IINVENTOR.

CLI DE I. CARR HARRY FRI EDMANN HAIG D TARPINIAN Dec. 29, 1970 c, R ETALMETHOD AND APPARATUS FOR MEASURING UNIFORMITY OF TIRES 8 Sheets-Sheet 2Filed Sept.

INVENTOR.

CLI DE LCARR HARRY FRIEDMANN HAIG D.TARPINIAN Dec. 29, 1970 c. l. CARRETAL 3,550,442

METHOD AND APPARATUS FOR MEASURING UNIFORMITY OF TIRES Filed Sept. 5.1968 8 Sheets-Sheet :5

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GLIDE LCARR HARRY FRIEDMANN HAIG D.TARPIN|AN (ONE REVOLUTION OF TIRE) C.l. CARR ET AL Dec. 29, 1970 METHOD AND APPARATUS FOR MEASURINGUNIFORMITY OF TIRES 8 Sheets-Sheet 4.

Filed Sept. 5, 1968 HARRY FRIEDMANN HAIG D.TARPINIAN Dec. 29, 1970 c,CARR ET AL 3,550,442

METHOD AND APPARATUS FOR MEASURING UNIFORMITY OF TIRES Filed Sept. 5,1968 8 Sheets-Sheet 5 START I I I I REsET FOR NExT .TEsT I WAITINGSAMPLE I READ-OUT I A PERIOD PERIOD PERIOD EBRI I W I UNIIFORMITY T Ax Tl I WAVE-FORM N ESPN 1% cfT w l I I OATED INPUT H I I TO OSCILLATOR I Il I I STEADY-STATE I SINE WAVE HARMONIG MAXIMUM VALUE MARK WAVE-FORMPEAK-TO-PEAK I I I\ I I I I VI J I I I I I I TIMING PULSES I IX ONWHITEILIGHT I I X I ON I AMBER LIGHT l I I xI I GALIBRATOR I I I XII IPRINT COMMAND INVENTOR. GLIDE I.OARR EHEZ HARRY FRIEDMANN T HAIGD.TARPINIAN m. 29, 1970 c, CARR ET AL 3,550,442

METHOD AND APPARATUS FOR MEASURING UNTFORMITY ()I" 'I'TRI'IS Filed Sept.5, 1968 8 Sheets-Sheet 6 I RESET q| Two -oc Q2 FROM IONTROLLER AIO 2 LIINVENTOR. T CLIDE LCARR HARRY FRIEDMANN CONTROLLER HAIG D.TARPINIANDec. 29, 1970 METHOD AND APPARATUS FOR MEASURING UNIFORMTTY OF TIRESFiled Sept. 5. 1968 8 Sheets-Sheet 7 PPM o4 FROM CONTROLLER TIMING JK lPULSES IKNVENTOR. o GLIDE LCARR HARRY FRIEDMANN HVAIG D. TARPINIAN Dec.29, 1970 c, RR ET AL 3,550,442

METHOD AND APPARATUS FOR MEASURING UNIFORMTTY OF TIRES Flled Sept. 5,1968 F I 7 8 Sheets-Sheet 8 $7 WAITING A SAMPLE READOUT PERIOD PERIODPERIOD PULSES START II 2 |3 4 I5 6 I I l I IRESET SIGNAL I D N2 I I l EJK3 I I NI I I I I F N6 (5 N3 I 1 l I N4 J T' N7 I l I J N5 I r" K 00COMPONENT INVENTOR.

CLI DE LCARR HARRY FRIEDMANN HAIG D..TARPINIAN United States Patent3,550,442 METHOD AND APPARATUS FOR MEASURING UNIFORMITY 0F TIRES ClideI. Carr, Grosse Pointe Park, Harry Friedmann, Huntington Woods, and HaigD. Tarpinian, Grosse Pointe, Mich., assignors to Uniroyal, Inc., NewYork, N.Y., a corporation of New Jersey Filed Sept. 5, 1968, Ser. No.757,663 Int. Cl. G01m 17/02 US. Cl. 73-146 17 Claims ABSTRACT OF THEDISCLOSURE Tire uniformity measuring method and apparatus wherein radialrunout on the outer tread rows is continuously averaged electrically asthe tire rotates to obtain a periodic electrical signal, the periodbeing equal to the time for one revolution of the tire. The periodicsignal is electronically analyzed with an analog oscillator circuit toobtain the maximum value of its first harmonic component and todetermine and mark the location of this maximum value on the tireitself. Associated circuitry and apparatus is disclosed.

The invention relates to a method and apparatus for obtaining tireuniformity measurements. More specifically, the invention relates to amethod and apparatus for measuring the radial runout of a tire and toapparatus for determining the magnitude of the first harmonic comoponent of such radial runout and for determining the location on thetire of the maximum value of the first harmonic component.

It is well known in the tire and automobile industries that tirenon-uniformity has a substantial adverse effect on the ride and handlingcharacteristics of the vehicles on which such tires are mounted. Forthis reason, methods were early developed for measuring tire uniformity.

One method for measuring tire uniformity involves the determination ofits radial runout. The term radial runout refers to the variation in theradius of the tire as measured when it is inflated but not under load.In order to measure radial runout, the tire may be placed on a wheel andaxle assembly and slowly rotated. As the tire rotates, its tread surfacecontacts an indicating mechanism, such as a dial indicator or adislpacement transducer, to thereby provide an indication of the radialrunout of the tire. It has been the practice in the tire industry tomake such radial runout measurements along and at or near thecircumferential centerline of the tread surface of the tire. While thismethod of measuring tire uniformity has the advantages of being simple,fast and inexpensive, it has the very great disadvantage of notproviding an adequate indication of tire performance and ridecharacteristics.

Another method for measuring time uniformity involves the measurement ofradial force variation of the tire while it is under load. Apparatusused in making this measurement includes a wheel and axle assembly onwhich the tire to be evaluated is mounted and also a test-wheel which isin contact with the tire. The tire is forceably held against thetest-wheel, the applied force thereby providing a predetermined load onthe tire, and when the test-wheel is rotated, the tire rotates with it.As the tire rotates the variation in the radial force on the axle onwhich the tire is mounted is measured. This radial force variationrepeats itself with each revolution of the tire. Because the radialforce variation repeats itself with each revolution of the tire, it maybe described mathematically as a continuous, bounded periodic function F(t) =F (t+r) where F(t) is the radial force variation as a function of3,550,442 Patented Dec. 29, 1970 time and -r is the period of rotation.Such a mathematical function may be expressed as a Fourier series, theterms of which may be combined by means of trigonometric identities toform the expression where the frequency w:21r/ 1-, 7' being the period;where 6, and 6,, are phase angles of the respective terms of theinfinite series; where C is a constant; where C is the amplitude of thefirst harmonic component of the periodic function F(t); and where Crepresents the amplitude of higher order harmonics. It has now beenfound by automotive and tire engineers that the value C of the firstharmonic component of radial force variation is an important factor tobe considered in the evaluation of tire uniformity with respect to theperformance and ride characteristics of the tire. Also the location onthe tire itself of the point at which the maximum value of the firstharmonic component of radial force variation occurs is of importance,knowledge of the location of this maximum value on each tire beinguseful in off-setting its undesirable effects. Although the measurementand determination of the location of the maximum value of the firstharmonic component of radial force variation provides a usefulindication of tire ride and performance characteristics, nevertheless,this method of uniformity measurement has the disadvantages of beingcumbersome and of requiring the use of expensive radial force variationmachines.

The method and apparatus of the present invention overcomes manydisadvantages of the past utilized radial runout and radial forcevariation. methods of measuring tire uniformity, and at the same time,combines their advantages to provide a rapid, adequate, accurate, andrelatively inexpensive method for measuring uniformity of tires asrelated to their performance and ride characteristics.

In accordance with one aspect of the invention, a method of measuringtire uniformity includes making radial runout measurementssimultaneously on the two outer tread portions or rows of a tire, thetwo measurements being made substantially in line with one anotheracross the tread width, and further includes averaging the twosimultaneously made measurements continuously as the tire is rotatedwith its tread surface in contact with measurement-sensing means. Witheach rotation of the tire, the average radial runout measurements arerepeated, and, thus, a periodic and bounded function F t) =F (t-I-r) isproduced. It has been found that there is a high degree of correlationbetween the first harmonic component of the average radial runout andthe same component of radial force variation. This correlation appliesboth to the maximum values of the respective first harmonic componentsand to the location at which those maximum values occur. Moreparticularly, it has been found that, for tires of the type normallyused on passenger cars, onethousandth of an inch of average radialrunout is approximately equivalent to one pound of radial forcevariation.

In accordance with another aspect of the present invention, apparatus isprovided for electrically averaging the radial runout on the outer treadportions or rows of a tire and to thereby obtain a periodic averageradial runout electrical signal which is, for one period only, fed intoan analog oscillator the output of which is proportional to the maximumvalue of the first harmonic component thereof. Moreover, circuit meansare provided for detecting the point on the tire at which such maximumvalue of the first harmonic occurs.

An understanding of these and further aspects of the invention may beobtained from a consideration of the following detailed description inconjunction with the appended drawings, in which:

FIG. 1 is a front elevational view of a simplified machine whichillustrates the method constituting one aspect of the invention;

FIG. 2 is an end elevational view of the machine of FIG. 1;

FIG. 3 is a sectional view taken along line III-III in FIG. 2, andillustrates measurement-sensing means which may be utilized to measureradial runout on the outer tread portions or rows;

FIG. 4 is a top view of the measurement-sensing means of FIG. 3;

FIG. 5 is a schematic diagram of a control circuit which may be used inconjunction with the simplified machine of FIGS. 1 and 2;

FIG. 6 contains various waveforms which illustrate the correlationbetween radial force variation measurements and measurements obtained byaveraging continuously the radial runout on tread outer portions orrows;

FIG. 7 is a block diagram of the computation circuits which are withinthe confines of the invention;

FIG. 8 illustrates waveforms that occur at various points in thecomputation circuits, the waveforms being designated by Roman numeralswhich also appear at the appropriate points in the block diagram of FIG.7;

FIGS. 9 through 19 provide detailed schematic circuit information as tothose items shown in block diagram form in FIG. 7, and are as follows:

FIG. 9-averaging circuit and filters;

FIG. 10DC suppression and gating circuit;

FIG. 11analog oscillator circuit;

FIG. 12harmonic amplitude detector and rejection level comparatorcircuits;

FIG. 13first harmonic maximum values location detector and relaycircuit;

FIG. 14-peak-to-peak detector circuit;

FIG. 15timing-pulse shaper;

FIG. l6sequence controller circuit;

FIG. 17outputs of sequence-controller-circuit elements with respect totiming pulses;

FIG. 18square-wave calibrator circuit; and

FIG. l9logic-monitor light circuit.

Referring now to the drawings and first to FIGS. 1 and 2, there is shownapparatus which illustrates in part the practice of the method whichconstitutes one aspect of the invention. A frame 1 has mounted thereonbearings 2 and 3 journalling axle 4 for rotational movement. Drive means5 are provided for slowly rotating axle 4, and wheel 6 affixed thereto,at a constant angular velocity, or speed. The tire T to be measured foruniformity is mounted on wheel 6. Measurement-sensing means 7a and 7bare provided for continuously contacting the outer tread portions orrows of the tire T.

FIGS. 3 and 4 are enlarged views of the measurement sensing means, andreference is now made thereto. A cylinder 8 is provided having endblocks 9 and 10 which, in turn, are secured to base plate 11. The endblocks 9 and 10 have bushings 12 and 13, respectively, mounted thereinand through which shaft 14 passes enabling it to move axially withrespect to cylinder 8. A stop 15 is attached to shaft 14 by means ofroll pin 16 and is adapted to limit the axial movement of shaft 14. Alsoattached to one end of shaft 14 is tie member 17 which has a slot in itthrough which rod 18 passes, the latter serving to prevent rotationalmovement of shaft 14. Tie member 17 also translates the axial movementof shaft 14 to the movable element 19 of displacement transducer 20(FIG. 2) which, preferably, is a linear motion potentiometer. At theother end of shaft 14, there is attached thereto a clevis 21 which has asmall roller 22 rotatably mounted between its forked parts.

Referring back to FIG. 2, it may be seen that measurement-sensing means7a and 7b are mounted on base plate 11 and that base plate 11 isattached to slide plate 23 which is adapted to slide in guide meansprovided in bracket 24 mounted on frame 1. Movement of slide plate 23,and, therefore, of measurement-sensing means 7a and 7b, toward and awayfrom tire T is accomplished with air cylinder 25.

The operation of the above apparatus will now be described with the aidof the control circuit shown in FIG. 5.

With the measurement-sensing means 7a and 7b held in retracted positionby air cylinder 25, tire T is mounted on wheel 6. Pushbutton FBI is thendepressed to simultaneously energize control relay CR1 and solenoidvalve SV-lA, the energization of SV-1A causing tire T to be inflatedthrough airline 26 (FIG. 1) which is attached to a suitable rotatablecoupling of the wheel and axle assembly. Next, pushbutton PB2 isdepressed to energize solenoid valve SV-2, which affects air cylinder 25to permit the measurement sensing means 7a and 7b to contact the treadsurface of tire T. Pushbutton PB2 also energizes time delay relay TDRwhich, in turn, locks itself in and energizes motor starter M1 whichcauses tire T to rotate. After a predetermined delay, during which theangular velocity of tire T becomes constant, timed contact TDR closescausing control relay CR2 to be energized and locked in by itsnormally-open contact. The normallyclosed CR2 contact opens and providesa signal to the computation circuits (described below) to initiateprocessing of the signals obtained from the linear potentiometers 20shown in FIG. 2. Throughout the period during which tire T rotates,timing pulses for the computation circuits are provided for each ofrotation of the tire; preferably, these pulses are obtained from amagnetic pick-up (FIG. 7) which produces a pulse when either of twoferrous protrusions 180 apart on the axle moves in proximity to themagnetic pick-up. A cam-driven limit switch could be utilized in lieu ofthe magnetic pick-up.

One of the functions of the computation circuits is to determine thelocation on the tire of the maximum value of the first harmoniccomponent of average radial runout. At the instant in time that themaximum value occurs, the computation circuit causes normally-open relaycontact RC2 (FIG. 5) to close, thereby, energizing tiremarker solenoidTM (FIG. 5 and FIG. 2) which places a mark on the tire tread surface.The computation circuit also causes normally-closed relay contact RC1 toopen; this de-energizes time delay relay TDR, solenoid SV-2, and motorstarter M1, and causes the tire T to stop its rotation and furthercauses the measurement-sensing means 7a and 7b to move away from thetire. Pushbutton PBS is then depressed to reset the control andcomputation circuits for the next tire uniformity measurement. Whenpushbutton PB4 is depressed, tire T deflates and may then be removedfrom wheel 6.

The simplified apparatus and control circuit therefor which have beenthus far described are primarily intended to be broadly illustrative ofthe method which constitutes a part of the invention. Apparatus is knownby the inventors to be commercially available which will automaticallymount and inflate a tire, start it rotating, actuate measurement-sensingmeans, and deflate and remove the tire. It is believed to be well withinthe skill of the art to adapt the present invention to such automaticapparatus.

It is now necessary to describe in much more detail the method ofmeasuring average radial runout and the computation circuits employed indetermining the maximum value and location of the first harmoniccomponent of average radial runout.

With the reference to FIG. 2, it may be seen that rollers 22 of therespective measurement-sensing means 711 and 7b are in contact with theouter tread portions or rows of tire T. As shown in FIGS. 2 and 3, theforce of gravity may be sufficient to gently urge roller 22 against thetread surface; however, it may be necessary to provide means, such asspring force, for urging the measurement sensing means against the treadsurface, as would be the case where the tire to be measured is mountedhorizontally rather than vertically as shown.

As tire T rotates, variations in its radius (radial runout) producecorresponding displacement variations in the respectivemeasurement-sensing means 7a and 7b which variations are, in turn,converted into electrical signals by means of linear motionpotentiometers 20. These variations are generally not the same on oneside of the tire as they are on the other side thereof, and, thus, thetwo electrical signals produced by the respective potentiometers 20 alsodiffer. The two signals may, however, be continuously averaged, usingcircuit means described below, to obtain an average radial runout.

electrical signal. This average radial runout signal is peri odic, witha period equal to the time for one revolution of tire T, because thevariations in tire radius are repeated with each revolution of the tire.

FIG. 6 contains four waveforms, labeled A, B, C and D, which wereobtained as a result of radial runout and radial force variationmeasurements made on a bias-ply, passenger-car tire. Waveform A showsone complete period of radial runout of the outer tread row on one sideof the tire only; waveform B shows a complete period of radial runout ofthe tread row on the opposite side of the tire; waveform C shows acomplete period of average radial runout of the tire, the average beingtaken by continuously adding together, as the tire rotates, the radialrunout measurements of both outer tread rows and then dividing the sumby two. To illustrate, if waveforms A and B are added together point bypoint and the sums averaged, then waveform C will be obtained.

Waveform D shows the tires radial force variation, measured in pounds offorce. Comparison of waveform C (shown double size), the average radialrunout, with waveform D establishes the similarity between the twomeasurements. Furthermore, it may be seen from the scales at the sidesof the waveforms that one-thousandth of an inch of average radial runoutis approximately equivalent to one pound of radial force variation. Thishigh degree of correlation between average radial runout and radialforce variation, which includes correlation of the maximum values andphase angles of the first harmonic components thereof, has been found toexist in a large quantity of tires examined for uniformity.

It was earlier stated that it is not the periodic average radial runoutthat is of primary interest in determining tire uniformity but, rather,the first harmonic component thereof. The computation circuits describedbelow provide the necessary information concerning the first harmoniccomponent of average radial runout. It must be mentioned here that thecomputation circuits, if desired, may also be used to determine thefirst harmonic component of a radial force variation signal.

FIG. 7 is a block diagram of the computation circuits and includesblocks designating the inputs to these circuits and the outputstherefrom. The Roman numerals which appear in the block diagramcorrespond to the waveforms so numbered in FIG. 8.

When the first harmonic component of average radial runout is beingdetermined, the signals from the linear motion potentiometers 20 arecontinuously combined and averaged by the averaging circuit to obtain aperiodic average radial runout signal which includes a DC component(waveform I). The DC component, which results from the DC voltageapplied across the linear motion potentiometers, is then removed by a DCsuppression circuit. This average radial runout signal is then amplifiedand, at the command of the sequence controller, gated for one period asshown by waveform II. The amplitude of this waveform is measured withthe peak-to-peak 6 detector and its output (waveform VI) is indicated onthe RUNOUT PP METER. The gated average radial runout signal is also fedinto the analog oscillator. The response of the analog oscillator to thegated input signal is transient during the sample period, but at thestart of the read-out period it becomes a steadystate sine wave andcontinues as such thereafter as shown by waveform III. The amplitude ofthis sine wave is proportional to the maximum value of the firstharmonic component of average radial runout and is measured by theharmonic amplitude detector. If desired, the output of the harmonicamplitude detector (waveform IV) may be fed into a rejection levelcomparator which cornpares the harmonic amplitude with a predeterminedreference value; if the harmonic amplitude exceeds such predeterminedvalue, the comparator may be used to indicate this fact, such as bymeans of turning on a rejection light, and also to operate automaticmeans, such as a gate in a conveyor system, for rejection of the tiremeasured for uniformity and found by the comparator to be unacceptable.In addition to being fed into the harmonic amplitude detector, the sinewave output of the analog oscillator is also fed into the harmonicmaximum-value location detector. This detector is of the negative-going,zero-crossing type, i.e., it detects the point, as shown by waveform V,at which the sine wave output of the analog oscillator crosses zero andthen becomes negative. This point corresponds, in time, to theoccurrence of the maximum value of the first harmonic component ofaverage radial runout, and the tire marker is energized at the instantthis point is reached.

The sequence controller governs the specific times during which theabove described operations take place. There are two inputs to thesequence controller. They are: (l) the reset signal, as shown bywaveform VII, which occurs when normally closed contact CR2 (FIG. 5)opens, and (2) timing pulses, as shown by waveform VIII, which areproduced every of rotation of the tire by the magnetic pick-up and whichare shaped by the pulse shaper. The entire sequence of operation of thecomputation circuits takes place within three tire revolutions. Thistime is divided by the sequence controller into three consecutiveperiods; the waiting period lasting for at least one-half revolution,the sample period lasting for one complete revolution, and the read-outperiod also lasting for one revolution. Waveform IX is produced by thesequence controller during the sample period and is fed to the DCsuppression and gating circuit; a suitable logic monitor light may beused to indicate the occurrence of this period. Waveform X is producedby the sequence controller during the read-out period and controlsoperation of the harmonic amplitude detector; a suitable logic monitorlight may also be used to indicate the occurrence of this period. Thesequence controller also produces a square wave, waveform XI, whichdrives the calibrator, and a print command signal, waveform XII, whichmay be used to energize an optional digital voltmeter-printer system.

The specific circuits shown in block diagram form in FIG. 7 aredescribed in detail in the paragraphs which follow.

The details of the summing circuit and filters are shown in FIG. 9. Inthis circuit, linear motion potentiometers 20 are shown in schematicform. A DC voltage is applied across the potentiometers, and thevoltages E and E from the respective arms thereof, these voltages beingthe radial runout signals from the respective outer tread portions ofthe tire being measured for uniformity, are applied across equal-valuedresistors 31, 32, 33 and 34. The output E is the average radial runoutsignal, including a DC component, and is equal to the sum of voltages Eand E divided by two. Capacitors 35 and 36 are included in the circuitfor the purpose of removing possible 60-cycle .pick-u p.

The average radial runout signal E becomes the input to theDC-suppression and gating circuit shown in FIG. 10. The DC-suppressionand gating circuit removes the DC component of signal E amplifies theremaining signal, and gates it for one period. Although the DC componentof signal E does not contain any harmonics, its removal is necessarybecause, otherwise, it would, upon amplification, cause the analogoscillator to saturate.

In FIG. 10, amplifier A3 is wired as an inverting, difference amplifier;its output E may be expressed as follows:

E r Es) where R /R is the gain. Amplifiers A1 and A2 act as currentamplifiers and have high input impedances and a unity voltage gainfactor. When switch S is closed, the input to amplifiers A1 and A2 issignal E and their respective outputs are equal, that is, E =E FromEquation 1, it may now be seen that the output of amplifier A3 will bezero when switch S is closed because the voltage difference of theinputs, E E is equal to zero. However, when switch S is open, the DCcomponent of the input signal E is stored in capacitor 37. This meansthat the output of amplifier A2 is the DC value of signal E and thatthis DC component is subtracted from signal E B, being equal inmagnitude to E by difference amplifier A3, which also amplifies thedifference signal. To summarize, when S is closed, the output E ofamplifier A3 is zero, but while S is open, output E is the differencebetween E and its DC component, this difference being amplified by afactor of R /R Gating of the output signal E is accomplished with switchS Both this switch and switch S are operated simultaneously by thesequence controller and are open only during the sample period.

The output voltage E of the DC suppression and gating circuit is fed tothe analog oscillator circuit which is illustrated in FIG. 11.

The analog oscillator circuit is the electronic analog of an undampedoscillator that obeys the equation 52( x( where F(t) is a forcingfunction, or input signal to the electronic analog, and is a function oftime;

is the second time derivative of (t); w is the natural frequency of theoscillator; and p is a gain factor on the input forcing function F(t).If the forcing function F(t) is periodic and bounded, as is a radialforce variation or average radial runout signal, then, as was previouslystated, it may be described by the Fourier series expression It may beshown mathematically that if such a forcing function is applied to theoscillator for one period only, such period being equal to 21r/w, thenthe response (t) of the oscillator to this forcing function F(t) will besin (amt-B 8 the first harmonic component C cos (wa l-6 of F(t) is atits maximum value.

It is necessary to state here that although the analog oscillatorcircuit described above and hereinafter has a natural frequency incorresponding to the first harmonic frequency of the periodic andbounded forcing function F(t), this nevertheless does not limit theoscillators usefulness to measurement of the first harmonic component ofsuch periodic and bounded forcing function F(t). Rather, if it isdesired to measure the amplitude and phase angle of a predeterminedhigher order harmonic component of forcing function F(t), then thenatural frequency of the analog oscillator circuit may be adjusted, withcircuit means hereinafter described, to correspond to the frequency ofsuch predetermined higher order harmonic. The oscillator would then bethe electronic analog of the equation where n designates the number ofthe predetermined higher order harmonic component being measured andWhere to would then be the fundamental frequency of the periodic andbounded forcing function F(t). If forcing function F(t) were to be gatedto the analog oscillator, for a single period only, as its input signal,then the analog oscillator response (t) would be As was earliermentioned, the analog oscillator circuit is the electronic analog ofEquation 2. When the gated average radial runout signal E is applied tothis circuit, this signal corresponds to the forcing function F(t) andthe analog oscillator output signal E is a sine wave the amplitude ofwhich is proportional to the maximum value of the first harmoniccomponent of the gated average radial runout signal B In FIG. 11,operational amplifier A4 is wired as a summing amplifier. Its output Eis where R and R are resistances, E is the input signal, and E is afeedback signal from the output of amplifier A6. Operational amplifierA5 is used as an integrator. Its output E is proportional to theintegral of its input E, that is,

where R is the value of resistor R, and C is the value of capacitor C.Operational amplifier A6 is also an integrator. Its output is where Rand C are resistance and capacitance values, respectively, associatedwith amplifier A6 and are of the same value as those indicated byEquation 6. Substituting the expression for E; from Equation 6 intoEquation 7 produces the result after differentiation twice, Equation 9becomes where Ilg is the second time derivative of E Substituting thevalue of E from Equation 5 into Equation 10 gives the equation R5 1 2 E5 i 2 R1(R c) J II R3 Rc Equation 11 may be seen to be the electronicanalog of Equation 2 wherein E corresponds to E corresponds to F(l),

hi w 7:. RC

cillator for a single period only, is also similar to that for Equation2, this solution being and E9: #01 Si11(wi+5 The natural frequency w ofthe oscillator can be adjusted by varying resistance R Since R does notappear in Equation 12, adjustment of the oscillator frequency in thisway does not affect the gain of the analog oscillator circuit. Suchadjustment is necessary to make the os cillator frequency equal to thefrequency of the average radial runout signal E which, in turn,corresponds to the angular frequency of the rotating tire being measuredfor uniformity.

In FIG. 11, the circuit elements enclosed by broken lines are the partsof a double-pole photocell-lamp combination. The resistive elements 41and 42 have a resistance, when they are not being exposed to light, ofabout 1000 megaohms, which does not affect the function of theintegrators. However, when transistor Q1 is rendered conductive by thereset signal (waveform VII of FIG. 8) then lamp L is lighted and thiscauses the resistance of elements 41 and 42 to decrease to about only500 ohms; this low resistance value permits capacitors C to dischargeand, thereby, restores the integrating circuits of the analog oscillatorto a quiescent state. Thus, the oscillator is automatically reset at thecompletion of each tire uniformity test and made ready for a subsequenttest.

The output signal E; from the analog oscillator circuit is fed into theharmonic amplitude detector circuit shown in FIG. 12. In this circuit,when transistor Q2 is rendered non-conductive by the signal from thesequence controller, diode D2 is reverse-biased since the saturationlevel of amplifier A6 precludes signal E, from exceeding the positive DCvoltage applied to diode D2 through resistor 43. However, diode D1permits capacitor 44 to be charged to the maximum value of E but blocksdischarge of capacitor 44 when E, begins to decrease in voltage level.The voltage across capacitor 44 is the input to operational amplifierA7, which is a unity gain amplifier having a high input impedance thatprevents appreciable leakage of charge from capacitor 44; the output ofamplifier A7 would be the maximum value of signal E were it not for thefact that the voltage across capacitor 44 differs by a small amount fromE due to the knee characteristic of diode D1. To compensate for this, asmall voltage is added to the output of amplifier A7 through resistor 47associated with operational amplifier A8 to which the signal fromamplifier A7 is fed. The output E of amplifier A8 represents thecorrected maximum value of the first harmonic. Signal E is designated aswaveform IV in FIG. 8.

Transistor Q3 is used to hold the harmonic amplitude meter AM at zerountil the beginning of the readout period at which time both it andtransistor Q2 are rendered nonconductive. Upon completion of theread-out period, transistors Q2 and Q3 become conductive once again.

When transistor Q2 is in the conductive state, diode D2 forms adischarge path for capacitor 44. Thus, the harmonic amplitude detectorcircuit is automatically reset for the next harmonic amplitudemeasurement.

The rejection level comparator circuit and the relay associatedtherewith are also shown in FIG. 12. The operational amplifier A9 iswired as a voltage comparator in that it compares signal E whichrepresents the harmonic maximum value, with a preset voltage, which isobtained from potentiometer 46 and which corresponds to the desiredrejection level. If signal E exceeds the preset rejection level, theoutput of amplifier A9 renders transistor Q4 conductive. This, in turn,places transistor Q5 in the conductive state and energizes a relayhaving a contact RC3 which may be used to operate an indicating lightand/or to operate automatic means, such as a gate in a conveyor system,for rejection of the tire measured for uniformity and found by thecomparator to be unacceptable because its first harmonic componentexceeded the preset rejection level. Diode D3, which is connected acrossthe relay coil, is used to provide a discharge path for any energy whichmay remain in the coil after transistor Q5 becomes nonconductive.

The circuit which appears in FIG. 13 is the first harmonic maximum valuelocation detector and relay circuit. The input to operational amplifierA10 is signal E; from the analog oscillator circuit, signal E being asine wave proportional in amplitude to the maximum value of the firstharmonic component of the analog oscillator input signal, but 1r/2radians out of phase with it. It is this phase difference which causesthe time at which E, crosses zero in a negative-going direction tocoincide with the maximum value of the first harmonic component. Thecircuit operation is such that each time signal E crosses zero,amplifier A10 becomes saturated, due to its very high gain, to either apositive or negative voltage level depending on the polarity of inputsignal E If E is negative-going when it crosses zero, then amplifier A10saturates to a positive voltage level; converse is true when E, ispositive-going. When amplifier A10 saturates to a positive voltagelevel, capacitor 51 converts this into a short positive pulse whichbriefly renders transistors Q6 and Q7 conductive and, thereby, energizesthe relay. When the relay is energized, its normally-closed contact RC1opens and its normally-open contact RC2 closes; as was previouslydescribed in connection with the discussion of FIG. 5, this actuatesmeans for marking the location of the maximum value of the firstharmonic on the tire itself. Diode D4 proides a discharge path for anyenergy which may remain in the relay coil after transistor Q7 becomesnon-conductive, Transistor Q8 is included in the circuit to prevent therelay from being energized except during the read-out period. Whentransistor Q8 is in its conductive state, transistor Q6 cannot berendered conductive by the positive pulses from capacitor 51, and thesequence controller holds transistor Q8 in such conductive state exceptduring the read-out period.

The circuit for the peak-to-peak detector is shown in FIG. 14. Thiscircuit is designed to measure the peak-topeak value of the averageradial runout or, as the case may be, radial force variation signalbeing fed into the analog oscillator circuit. The input to thepeak-to-peak detector is signal E This signal is applied to twoessentially separate peak detectors, one for detecting the maximum valueand the other for detecting the minimum value. These peak detectorsfunctions in a manner similar to that of the previously describedharmonic amplitude detector. When transistor Q9 is in a non-conductivestate, its collector is at a positive DC voltage which is in excess ofthe saturation level of amplifier A3 (FIG. 10), the output of which issignal E Because the voltage on the collector of transistor Q9 exceedsthe input voltage E diode D7 is reverse-biased. This permits capacitor52 to be charged to the maximum value of signal E diode D5 and the highinput impedance of unity-gain operational amplifier A11 prevent loss ofthe charge built up on capacitor 52. In a similar manner, the minimumvalue of signal E is stored by capacitor 53 through the actions oftransistor Q10, reverse-biased diode D8, diode D6 and unity-gainoperational amplifier A12. The peak value outputs E and E of amplifiersA11 and A12, respectively, are connected across peak-to-peak meter PPM.Variable resistor 54 is used to adjust the gain of the meter. Aconductive state in transistor Q9, initiated by a signal from thesequence controller, causes transistors Q10, Q11 and Q12, to conduct,thereby, shunting off the outputs of amplifiers A11 and A12 andpermitting capacitors 52 and 53 to discharge through diodes D7 and D8which are then biased to ground through transistors Q9 and Q10,respectively. This resets the peak-to-peak detector circuit for the nextmeasurement.

In FIG. 15, the timing-pulse shaper circuit is illustrated. As waspreviously mentioned, the timing pulses for the sequence controller arepreferably derived from magnetic pick-up means which produces a pulsefor every 180 of rotation of the tire being measured for uniformity.Such pulses do not, however, have a sufficiently rapid fall time totrigger the controller circuit which requires that the fall time be lessthan 100 nanoseconds. To achieve this rapid fall time, the pulses E fromthe magnetic pick-up are fed into high-gain amplifier A13. In order toprevent amplifier A13 from responding to possible noise signals, it issupplied with a reference voltage input E obtained from potentiometer55; this reference voltage sets the trigger level of amplifier A13. Whenthe pulse voltage E exceeds the preset reference voltage E thenamplifier A13 produces an output which renders transistor Q13conductive. This produces a sufficiently rapid drop in the outputvoltage E taken at the collector of transistor Q13, as is illustrated bythe voltage diagram shown in FIG. 15. When the input pulse E again dropsbelow reference voltage E transistor Q13 ceases to conduct therebycausing a sudden rise in output voltage E The shaped pulses thusproduced are fed into the sequence-controller.

The sequence-controller circuit appears in FIG. 16. This circuitcontrols the sequence of events which occur in the various computationand output circuits. Preferably, the entire sequence-controller circuitis constructed with integrated circuit components. In FIG. 16, J K1, JK2, and JK3 are integrated J-K type circuit flip-flop components, and N1through N7 are integrated circuit NOR- gate components. The upper caseletters A through K, which appear at output locations of the variousintegrated circuit components, designate the respective outputs of thesecomponents and correspond to the letters which appear at the right-handside of the waveforms shown in FIG. 17. In FIG. 17, the designations forthe components which have the outputs indicated are placed at thelefthand sides of the waveforms. The timing pulses and reset signalwaveform are also shown in FIG. 17 to indicate the time relationships ofthe various waveforms to one another. Waveforms VII through XII of FIG.8 correspond to waveforms labeled reset signal, timing pulses, G, H, Band K, respectively, in FIG. 17.

There are two inputs to the sequence controller circuit: the resetsignal obtained from normally-closed contact CR2 in the previouslydescribed machine control circuit, and periodic pulses E obtained fromthe timingpulse shaper circuit (FIG. With these inputs, the sequencecontroller provides output B which drives the calibrator, output G whichoperates the DC suppression and gate circuit, output F which controlsthe operation of the harmonic amplitude detector, output I which enablesthe harmonic maximum-value detector to operate, output I which controlsthe waveform peak-to-peak detector, and output K which may be used toactuate a digital voltmeter-printer system upon termination of: eachtire uniformity measurement.

Further details of the sequence controller circuitry and operation arenot presented herein since these are believed to be well within theknowledge of persons skilled in the art of digital logic circuit design.

As was stated above, output B from the sequence controller drives thecalibrator, the circuit diagram for which appears in FIG. 18. Output Bis a square wave generated as a result of the timing pulses which occurwith each of tire rotation. The calibrator circuit is simply atransistor switch circuit the output E of which is also a square wavehaving a DC component. Square wave B is used to calibrate the overallgain of the DC suppression and gating, the analog oscillator, and theharmonic-amplitudemeter circuits. As is shown in FIG. 7, the square-wavecalibration signal is applied to the input of the DC suppression andgating circuit, which removes its DC component leaving only the squarewave portion. Because the amplitude of the first harmonic component of asquare wave is known to be equal to 4/11- times the square waveamplitude, the square wave calibration signal may be made the input tothe analog oscillator and the gain of the harmonic amplitude meter maythen be adjusted so that a chosen meter scale reading corresponds to theamplitude of the first harmonic component thereof. Furthermore, if thesquare-wave amplitude is initially tailored, by proper choice ofresistance values in the calibrator circuit, to correspond to a certainnumber of inches of average radial runout or pounds of radial forcevariation, then the harmonic amplitude meter will be capable of beingread directly in such units.

The square-wave calibration described above is dependent upon thepresupposes correct frequency calibration of the analog oscillatorcircuit. The natural frequency w of the analog oscillator mustcorrespond to the angular frequency of the rotating tire. Such frequencycorrespondence is achieved through use of the fact that the out put ofthe analog oscillator will theoretically be zero if a DC-voltage inputis gated to it for a time equal to one period at the natural frequency wof the oscillator. A regulated DC voltage is gated to the analogoscillator circuit for one period at the rotational frequency of thetire. If the output of the analog oscillator, which may be measured withharmonic amplitude meter AM, is then not equal to zero, adjustment ofvariable resistance R (FIG. 11) is made until the output is as nearlyequal to zero as possible. At this point, the natural frequency w of theanalog oscillator corresponds to the angular frequency of the rotatingtire.

With reference now to FIG. 19, therein illustrated is a circuit whichmay be used to provide a visual indication of the occurrence in thecomputation circuits of either the sample or read-out periods. If thesample period is being monitored, then waveform G (FIG. 17) from thesequence controller is the input; if the read-out period were beingmonitored, then waveform H would be the input. If it is assumed that thesample period is being monitored, then, during this period, transistorsQ14 and Q15 are rendered conductive. This causes lamp L1 to light and toremain in that condition until the end of the sample period.

While there has been described above a presently preferred embodiment ofthe method and apparatus of the invention, the invention is notrestricted to the specific structural details and circuit connectionsherein set forth, as various modifications thereof may be effectedwithout departing from the spirit and scope of the invention and theclaims thereto.

The invention having thus been described, what is claimed and desired tobe protected by Letters Patent is:

1. In the method for measuring the uniformity of a tire by determiningits radial runout, the improvement which comprises:

(a) measuring the radial variation on the outer tread portions of thetire; and

(b) averaging the measurements made on said outer tread portions, theaveraged measurements being those made on the tread surfacesubstantially in line with one another with respect to a line parallelto the axis of rotation of the tire.

2. In the method for measuring the uniformity of a tire wherein the tireis mounted for rotation about its own axis, inflated, rotated, and itsradial runout measured, the improvement which comprises:

(a) simultaneously and continuously, as the tire rotates at a constantangular velocity, measuring its radial runout at points substantially inline with one another across the tread width and on the two outerportions thereof; and

(b) continuously averaging the outer tread portion radial runoutmeasurements thus obtained.

3. In the improved method of claim 2, the additional steps ofelectrically obtaining a periodic and bounded average radial runoutsignal; and

electronically analyzing said signal to determine the maximum value, andthe location thereof on the tire, of the first harmonic component ofsaid signal.

4. A method for measuring the uniformity of a tire,

which comprises:

(a) mounting the tire for rotation about its own axis;

(b) inflating the tire;

(c) rotating the tire at a constant angular velocity;

((1) contacting the two outer portions of the tread surface of the tirewith measurement-sensing means capable of measuring the respectiveradial runouts on said two outer tread portions, said measurementsensingmeans having movable elements located substantially in line with oneanother across the tread width and which contact the tread surface;

(e) with the movable elements of said sensing means, simultaneouslymeasuring the radial runouts of the tire on the outer tread portionsthereof;

(f) as the tire rotates at said constant angular velocity,

continuously averaging the radial runout measurements obtained from theouter tread portions of the tire;

(g) deflating the tire; and

(h) dismounting the tire.

5. In the method of claim 4 and prior to deflating and dismounting thetire, the additional steps of:

electrically obtaining a periodic and bounded average radial runoutsignal; and

electronically analyzing said signal to determine the maximum value andthe location thereof on the tire of the first harmonic component of saidsignal.

6. The method of claim 5, including the additional step of marking onthe tire the location of the point at which the maximum value of thefirstharmonic component of said average radial runout signal occurs.

7. A method for measuring the uniformity of-a tire, which comprises:

(a) mounting the tire to be measured for uniformity on a wheel to enableit to be rotated about its own axis;

(b) inflating the tire so mounted;

(c) bringing two measurement-sensing means into contacting engagementwith the two outer tread portions of the tire, said measurement-sensingmeans being located substantially in line with one another across thewidth of the tread surface;

(d) rotating the tire at a constant angular velocity;

(e) as the tire rotates, simultaneously measuring the radial runout onthe outer tread portions of the tire;

(f) as the tire rotates, continuously averaging the outer tread portionradial runout measurements thus obtained;

(g) deflating the tire; and

(h) removing the tire from said wheel.

8. The method of claim 7, wherein the step of continuously averaging theouter tread portion radial runout measurements is performed withelectrical circuit means by which a periodic and bounded average radialrunout electrical signal, having a period equal to the time for onerevolution of the rotating tire, is obtained.

9. The method of claim 8, including the additional step ofelectronically measuring the amplitude and phase angle of the firstharmonic component of said periodic and bounded average radial runoutelectrical signal.

10. The method of claim 9, including the additional step of marking onthe tire the location of the point at which the maximum value of thefirst harmonic component of average radial runout occurs.

11. Apparatus for obtaining a periodic and bounded electrical signalrepresentative of the average radial runout of a tire, which comprises:

(a) means for rotating the tire at a constant angular velocity;

(b) means for measuring the radial runout of the tire, as it rotates atsaid constant angular velocity, on its two outer tread portions;

(c) circuit means for continuously averaging, as the tire rotates, thetwo outer tread portion radial runout measurements;

whereby a periodic and bound-ed average radial runout electrical signalis obtained.

12. Apparatus in accordance with claim 11, wherein said circuit meansfor continuously averaging, as the tire rotates, the two outer treadportion radial runout measurements comprises:

two linear potentiometers having movable arms responsive to therespective outer tread portion radial runout measurements, said linearpotentiometers being connected in parallel and having a DC voltageapplied thereto; and

equal-valued resistance means to continuously provide an output voltageequal to the average of the voltages on the arms of said linearpotentiometers.

13. Apparatus in accordance with claim 12, wherein said means formeasuring the radial runout of the me on its two outer tread portionscomprises:

a base plate positioned in spaced relation with respect to the locationfor the tire to be measured; and

a pair of sensing means attached to said base plate, each of saidsensing means having movable elements capable of continuouslycontracting the tread surface of the tire to be measured as it rotates,each of said sensing means being positioned on said base plate to permitthe movable elements thereof to contact one of the outer tread portionsof the tread surface of the tire to be measured and to permit themovable elements to respond to the radial runout of the tire at each ofthe outer tread portions, the movable elements of each of said sensingmeans being attached to the respective arms of said linearpotentiometers whereby such arms are made responsive to the respectiveradial runouts of the outer tread portions of the tire.

14. Apparatus for measuring the uniformity of a tire,

which comprises:

(a) means for rotating the tire at a constant angular velocity;

(b) means for measuring the radial runouts of a tire on its two outertread portions;

(c) circuit means for continuously averaging, as the tire rotates, thetwo outer tread portion radial runout measurements thereby to obtain aperiodic and bounded average radial runout signal of angular frequency wand having a DC component;

((1) circuit means for suppressing the DC component of the averageradial runout signal and for gating the thus suppressed signal for asingle period;

(e) an electronic circuit means analog of the equation the input to saidelectronic circuit means analog being the gated average radial runoutsignal and corresponding to F(t) which is a function of time t, p

being a gain factor, the output of said electronic circuit means analogcorresponding to (t) and being a sine wave signal proportional inamplitude to the maximum value of the first harmonic component of theaverage radial runout signal, 560) being the sec- 16. Apparatus inaccordance with claim 14, which further comprises:

(i) circuit means for measuring the peak-to-peak value of the periodicand bounded average radial runout signal;

nd time derivatives of the output U), and to being (j) circuit means forcomparing the amplitude of the the natural frequency of said electroniccircuit means sine wave output signal with a predetermined reanalog;jection level value; and

(f) circuit means for measuring the amplitude of the (k) circuit meansfor controlling the'sequence of opersine wave output signal; ationsperformed by the various circuit means (d),

(e), (f), (g), (i); (j) hereinabove included.

17. Apparatus in accordance with claim 14, which further comprises:

circuit means for suppling a calibration signal for calibration of theoverall gain of circuit means (d), (e) and (f) of claim 14; and

circuit means for supplying a DC voltage, gated for a single period atthe angular frequency of the rotating tire, to said electronic circuitmeans analog to permit adjustment of its natural frequency to correspondto the angular frequency of the rotating tire.

(g) circuit means for determining the phase angle of the sine waveoutput signal, such phase angle being 1r/2 radians out of phase with themaximum value of the first harmonic component of the average radialrunout input signal and therefore indicative of its 1 phase angle; and

(h) means for marking 011 the tire the location of the maximum value ofthe first harmonic component of average radial runout.

15. Apparatus in accordance with claim 14, wherein said electroniccircuit analog comprises:

a first operational amplifier operative as a summing amplifier;

a second operational amplifier operative as an integrator and having asits input the output from said first operational amplifier; and

a third operational amplifier operative as an integrator and having asits input the output from said second operational amplifier, the outputfrom said third operational amplifier constituting a feedback input tosaid first operational amplifier.

References Cited UNITED STATES PATENTS DONALD O. WOODIEL, PrimaryExaminer

